This invention relates to new coupling agents for use in preparing star-block polymers and copolymers by solution polymerization or copolymerization of conjugated dienes and monovinyl aromatic monomers with alkyllithium initiators.
Highly branched block copolymers, sometimes called star-block copolymers, are old in the art of anionic polymerization. These star-block copolymers are prepared by first forming linear block polymers having an active lithium atom on one end of the polymer chain. These active, linear polymer chains are then coupled by the addition of a polyfunctional compound having at least three reactive sites capable of reacting with the carbon to lithium bond on the polymer chains to add the polymer chain onto the functional groups of the compound.
Zelinski, U.S. Pat. No. 3,280,084, polymerized butadiene with butyllithium initiator to form B-Li blocks (where B is polybutadiene) which when coupled with 0.02 to 1 part by weight per 100 parts of monomers of divinylbenzene gave star-block copolymers having polydivinylbenzene nuclei and several identical arms of polybutadiene branching therefrom. The arms can also be either random or block copolymers of styrene and butadiene (from A-B-Li blocks, where A is polystyrene segment) where the diene is the major component.
Zelinski, U.S. Pat. No. 3,281,383, teaches similar star-block copolymers to those in U.S. Pat. No. 3,280,084, except that coupling agents such as polyepoxy compounds, polyacids, polyaldehydes, etc., are used.
Childers, U.S. Pat. No. 3,637,554, prepares rubbery star-block copolymers having nuclei formed from polyepoxides, polyisocyanates, polyimines, etc., and identical arms from B-Li and A-B-Li.
Fetters et al, U.S. Pat. No. 3,985,830, discloses a product having a nucleus of more than one molecule of m-divinyl-benzene and at least three polymeric arms, each being a block copolymer of conjugated diene and monovinyl aromatic monomers wherein said conjugated diene block is linked to said nucleus.
Kiovsky, U.S. Pat. No. 4,077,893, teaches the use of various coupling agents to prepare lubricating oil additives. Among those coupling agents mentioned is ethyleneglycoldimethacrylate.
Bean et al, U.S. Pat. No. 4,304,886, prepares mixtures of star-block copolymers by coupling lithium metal-terminated polymers or copolymers with a mixture of two different coupling agents having different functionality.
Udipi, U.S. Pat. No. 4,309,517, teaches to use hydrocarbyl esters of N-cyclopropyl-N-hydrocarbylcarbamic acids as coupling agents.